# L'O.G.

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Using accumarray to sum all values associated with a given node
Given a graph with the following edges edges = [1 2; 2 3; 3 1; 2 4; 4 5; 4 1]; I have some data associated with each edge dat...

4 mois il y a | 2 réponses | 0

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Numerical first derivative of irregularly spaced data
Given a vector x and a vector y, the numerical first derivative should be gradient(y)./gradient(x) for all points specified by x...

6 mois il y a | 1 réponse | 0

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Solving an initial value problem when one of the initial values is unknown
I am trying to numerically solve the ODE given by a*y"(t) + b*y'(t) = c, where a, b, and c are positive constants. I set this up...

8 mois il y a | 2 réponses | 0

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How do you set up an ode solver with a more than one function in the ode?
For example, if you have an ode such as a*df(t)/dt + b*dg(t)/dt + f(t) + g(t) + c = 0 that you'd like to solve and if you want t...

8 mois il y a | 2 réponses | 0

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How do you solve a coupled ODE when one of the ODE results in a vector of length 3 and the other results in a scalar of length 1?
For instance, in the following example that I found online, if dz(2) were actually a vector, how would you modify this? [v z]...

8 mois il y a | 1 réponse | 0

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How to call an ode solver within another function?
I solve dx/dt = x(t) using an ode solver sol = ode45(@(t,x) u(t,x,ode,eps,a0),[t0 tf],[x1;x2]); that calls a function u fo...

8 mois il y a | 1 réponse | 0

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How to do this unusual Fourier transform?
I am trying to compute a sine transform: I'm not sure about the non-standard bound of the integral (why it's not infinity...

9 mois il y a | 1 réponse | 0

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Solving linear systems in Matlab
How do I solve for x in u = A(x+b)? A is a matrix, and the other terms are vectors. Isn't it something like x = A\u - b ? I'm no...

9 mois il y a | 2 réponses | 0

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Runge-Kutta with a function that changes at each time step
I previously asked a question about solving an equation dx/dt = u(x,t) where u(x,t) is a velocity. I want to solve for the posit...

9 mois il y a | 1 réponse | 0

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Using Runge-Kutta in Matlab
I am trying to solve an equation dx/dt = f(x,t) where f(x,t) is a velocity. I want to solve for the positions x to obtain the tr...

9 mois il y a | 1 réponse | 0

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Question

Integrating a constant?
This is more of a physics question than a Matlab question, but given an instantaneous velocity vx and a time increment dt, how d...

10 mois il y a | 1 réponse | 0

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Question

Numerical integral where the bounds change with each evaluation
I'm trying to take the following integral: I tried this symbolically, but I think that was throwing me off. I am attachin...

environ un an il y a | 1 réponse | 0

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How to take an integral symbolically and then convert it to type double?
How do I take the following integral symbolically? And convert it to double? I have a 1000 x 1 numeric vector of type double for...

environ un an il y a | 1 réponse | 0

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Inverse of a matrix
I want to solve the following for X2: A = B(X1+X2) where B is a matrix, and A, X1, and X2 are vectors. I can't divide by a matri...

environ un an il y a | 1 réponse | 0

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Integration when some of the values change over time
I have a function of the form where is the position of the k-th object and is the corresponding force. The force has a functio...

environ un an il y a | 1 réponse | 0

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Question

How can I detect the object in this noisy image?
I'm trying to process images like the attached. In this case, there should be an object near the center of the image around test...

environ un an il y a | 2 réponses | 0

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Question

Cell arrays with a vector within a cell within a cell
I have a cell array where each element consists of a 1 x 1 cell containing a vector of type double, i.e., C{1,1} contains a vect...

environ un an il y a | 3 réponses | 0

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How do you convert the cell within a cell to a vector?
I have a cell of cells. The inner cell is a 1 x 1 and contains a vector. The vector in each inner cell might be of different len...

environ un an il y a | 1 réponse | 0

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How to output a cell array as a table where the arrays contain vectors of different length?
I have a cell array C that is 3 x 10, with each element containing a vector of numbers of type double. Each vector is of a diffe...

environ un an il y a | 2 réponses | 0

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Working with cell arrays
I would like to separate columns in an array based on the unique values of the first column. I think the way to do this is a cel...

environ un an il y a | 1 réponse | 0

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How do I read each frame of a video?

environ un an il y a | 2 réponses | 0

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Finding first value in an array equal to each number in a vector
I can find the first value in test_array that is equal to 2 using the following: find(test_array==2, 1, 'first') But how d...

environ un an il y a | 1 réponse | 0

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Question

What is the previous syntax for this function?
I can combine strings using something like str = append("Hello","world") But I have access only to Matlab 2018a. The append fu...

environ un an il y a | 1 réponse | 0

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Question

How to remove repeating entries from a vector?
How do you remove repeating entries in a vector? For example: A = [1 1 1 0 0 1 1 1 1 0 0 0 0 0] should return B = [ 1 0 1 0]....

environ un an il y a | 1 réponse | 0

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Question

Vectorization problem for grouping entries in an array
The data below are grouped into three different subgroups based on the value of B(:,3). If, however, B(:,2) <= 1, how do I indic...

environ un an il y a | 1 réponse | 0

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How do you reshape an array to preserve the order in each row of the original array?
How do you reshape an array into a 1-dim column such that the first row of the original array is the first set of numbers in the...

environ un an il y a | 1 réponse | 0

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How do you set entries in a matrix for odd rows with odd columns to zero?
I want to set A(i,j) = 0 if both i and j are odd. Is this possible to do vectorially?

plus d'un an il y a | 1 réponse | 0

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How do you make the diagonal and certain off-diagonal elements of a matrix zero?
I have a square matrix and would like to make the diagonal elements zero, as well as select elements that are off-diagonal. For ...

plus d'un an il y a | 2 réponses | 0

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x values when taking a numerical derivative
I want to calculate the first derivative f(x) = dy/dx for data that is irregularly spaced in x. I think (correct me if I'm wrong...

plus d'un an il y a | 5 réponses | 0

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Changing the position of a plot
How do you move everything in a figure (plot, axes, axis labels) up while preserving the aspect ratio of the plot? It seems I ca...

plus d'un an il y a | 1 réponse | 0

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